Process for preparing fine powder polyurea and greases therefrom

ABSTRACT

Polyurea compounds are prepared by reacting amines and polyisoyanates in the presence of a liquid diluent in a high-pressure impingement mixing device under conditions sufficient to produce polyurea compounds having the consistency of a powder and in which diluent is dispersed.

This application is a divisional of U.S. application No. 11/656,796filed Jan. 23, 2007, now U.S. Pat. No. 7,923,421 B2, which claims thebenefit of U.S. Provisional Application No. 60/761,805 filed Jan. 24,2006.

FIELD OF THE INVENTION

The present invention relates to the manufacture of polyurea powder andthe manufacture of greases therefrom.

BACKGROUND OF THE INVENTION

Industrial lubricating greases are homogeneous products of semi-liquidto solid consistency. Essentially, they consist of a dispersion of athickener in a liquid lubricant or base oil. In general, the thickeneris a significant determinant of the properties of the greases.

Polyurea compounds are among the thickeners used in making greases.Often the polyurea compounds are prepared directly in the base oil bythe reaction of amines with isocyanates.

One method to test the performance of greases is cone penetration andprolonged working of lubricating greases through ASTM D217. A cone ofspecified weight is allowed to fall into a lubricating grease sample at25° C. The depth of the cone, in tenths of a millimeter, identifies theconsistency of the grease. With the use of Table 1, the NLGI grade ofthe grease is identified from the 60 stroke worked penetration.

TABLE 1 NLGI Classification Scale NLGI Grade ASTM Worked Penetration 000445-475 00 400-430 0 355-385 1 310-340 2 265-295 3 220-250 4 175-205 5130-160 6  85-115

This test can be used to determine the mechanical stability of a greasethrough prolonged working, such as 10,000 or more double strokes usingthe motorized grease worker. While cone penetrations are typicallyconducted at 25° C., measurements can be carried out at othertemperatures. About 300 grams of grease are required to conduct the ASTMD217 test. ASTM method D1403, DIN 51 804, and IP 310 describe conepenetration equipment commonly referred to as ½ and ¼ scale devices foruse when less than 300 grams of grease are available.

Dropping point of lubricating greases is used to determine hightemperature structural grease properties related to the thickener. InASTM D2265, the dropping point of a lubricating grease is thetemperature at which the thickener can no longer hold the base oil. Someof the reasons oil can no longer be held are that the thickener hasmelted or the oil has become so thin it is not held by the thickener.Grease is placed in a small cup and heated in an oven-like device. Whena drop of oil falls from the lower opening, the dropping point of thegrease is calculated using the temperatures in the oven and inside thecup. Soap or polymer thickened greases demonstrate a dropping pointwhile inorganic thickeners such as clay or graphite may not have adropping point.

In U.S. Pat. No. 5,314,982 there is disclosed a process for makingpolyurea greases by first making a dry polyurea compound. Then thecompound is pulverized to give powders having particles in the 100 to400 micron range. Thereafter, a paste of the powder and base oil isheated, cooled and homogenized in a high pressure homogenizer atpressures of 400 to 1500 bar.

In U. S. Pat. No. 6,498,130 B2 a grease having low noise characteristicsis made by shearing a base oil and thickener to reduce the thickenerparticles below about 500 microns in size. In this instancehomogenization is achieved at about 2000 psi.

Both the above mentioned patents show the desirability of using polyureaof small particle size. They also illustrate that the conditions underwhich the polyurea particles are prepared impact subsequent processingconditions such as the homogenization step in grease forming.

User demand for polyurea greases has been increasing steadily; however,manufacturing such greases has been more difficult and expensive whencompared to the manufacture of other greases.

One of the difficulties in manufacturing polyurea greases isconsistently obtaining on an industrial scale substantially uniformlyfine polyurea powder that is readily dispersible in a lubricating baseoil.

Accordingly, one object of the present invention is to provide a processfor making fine polyurea powder without the need for shearing orpulverizing large polyurea particles.

Another object of the invention is to provide a process for making finepowdered polyurea compounds which can be practiced on an industrialscale and that can be homogenized under standard grease homogenizingconditions.

Yet another object of the invention is to provide an improved method forpreparing polyurea greases thus greatly reducing the risk (hazards)associated in manufacturing with neat amines or isocyanates.

These and other objects of the invention will become more apparent fromthe following description.

SUMMARY OF THE INVENTION

Broadly stated, polyurea compounds are prepared by reacting amines andisocyanates in the presence of a liquid diluent in a high-pressureimpingement mixing device under conditions sufficient to producepolyurea compounds having the consistency of a powder and in whichdiluent is dispersed.

An embodiment of the invention comprises passing the powder formedthrough a containment zone having means for monitoring and controllingthe process.

Other embodiments and aspects will be clear from the following

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram of the machine device used to make polyurea.

FIG. 2 is a microphotograph of a polyurea particle made by impingementprocessing washed free of lubricating medium.

DETAILED DESCRIPTION OF THE INVENTION

In the practice of the invention primary amines and isocyanates arereacted to form polyurea compounds.

The amines include aliphatic, alicyclic, aromatic amines and mixturesthereof. Examples of such mono amines include pentylamine, hexylamine,heptylamine, octylamine, dodecylamine, cyclohexylamine, benzylamine,aniline, diamnes and the like.

Suitable isocyanates are selected from the group consisting ofpolyisocyanate, monoisocyanate, and diisocyanate, and any combinationthereof. Preferably, a diisocyanate is used. Furthermore, the isocyanatecomponent may be aliphatic or aromatic and preferably is selected froman aromatic diisocyanate or mixtures of aromatic diisocyanates. Examplesof such diisocyanates are phenylene diisocyanate, toluene diisocyanate,methylene diphenylene diisocyanate and the like. Typically, the aminesand isocyanates are reacted in mole ratios of about 1:1 to about 2:1 andgreater.

In the invention an amine and isocyanate is reacted in the presence of aliquid diluent in a high-pressure impingement mixing device such asimpingement device 10 shown in FIG. 1.

The liquid diluent employed in the practice of the present invention isone which is inert to the amines and/or isocyanates and is compatiblewith the components of any end product to be formed from the polyurea.Thus, in instances where the polyurea product is to be used as a greasethickener, a lubricating base oil suitable to grease formulations is apreferred diluent. Additionally, it is preferred that the amine orpolyisocyanate be readily soluble in the diluent. In general, it ispreferred to dissolve the amine in a base oil and preferably naphthenic,paraffinic, PAO, PAG and ester fluids can be used singularly or incombination as a diluent for either component individually orsimultaneously. Also, any carbon base solvents that are compatible witheither of the two components can be used as a diluent.

The amount of diluent used is not absolutely critical and will depend toa certain extent upon the solubility of the reactant, e.g., the amine inthe diluent. Indeed, in the present invention, it is preferred todissolve the amine in the diluent. Again, the diluent is not subjectedto just amine alone but can be combined with the isocyanate. At leastsufficient diluent is used to dissolve (disperse) the amine, andpreferably, the amount of diluent will be sufficient to provide asolution having about the same density as that of the isocyanate orpolyisocyanate—diluent combination. In the case where a naphthenic oilis used as diluent for the amine, the weight ratio of oil to amine willbe about 1:1 to about 1:3.

Experience has shown that in the absence of diluent, the impingementdevice plugs almost immediately, and the polyurea formed typically has asignificant amount of unreacted isocyanate groups, a result which is notdesirable.

Referring to the FIG. 1, isocyanate contained in vessel 11 is fed vialine 12 to impingement device 10, while primary amine and diluentcontained in vessel 14 is fed via line 15 to impingement device 10.

Means (not shown) are provided for regulating the flow of reactants fromtheir respective vessels through orifices in the impingement device 10(mix chamber) where the components are impinged and reacted.

The reactants are fed to impingement device 10 (mix chamber) underconditions sufficient to produce a polyurea compound having theconsistency of a powder and in which diluent is dispersed. The fluidcomposition of the solution or emulsion can be from 0.5:1 to 4:1 byweight of diluent to component. As presented in Lazer Light Scatteringanalysis performed for particle size determination, the polyureacompound will comprise particles between 700 to 10 microns with astandard size being 200 microns.

Conditions that impact the size of the particles produced include thereactor orifice size (dimensions of the mix chamber), flow rates,pressure, individual component temperature and reactant residence time.

The flow rates of the reactants are typically in the mole ratio rangedescribed above.

The reactor orifice size for the amine and diluent and isocyanatestypically will be different from that for the diisocyanate and generallywill be chosen for facilitating the metering of the reactants in theappropriate mole ratio. Typically, the reactor orifice diameter willrange from about 0.030 to about 0.150 inches; however, the reactororifice diameter for the amine/diluent feed generally will be largerthan that for the isocyante.

The pressure at which the reactants are fed into the impingement devicetypically will be above 500 psig and preferably 1000 psig to 1800 psig,while the temperature at which they are fed may range from about 0° C.to about 100° C. and preferably 24° C. to 55° C. The reactant residencetime is a function of reactant feed rate and reactor volume, i.e.,specified design of the mix chamber, the adjustment of which is wellwithin the skill of a routiner in the art.

In one embodiment the fine powdered polyurea formed in impingementdevice 10 falls through a containment zone 16 as shown in the FIG. 1.The containment zone 16 may be and preferably is equipped with anantistatic device 17. The finely divided powdered polyurea then may becollected on a conveyer belt system 18 for delivery to hopper 19 fromwhich it can be automatically fed to packaging material 20, such as,bags, boxes or the like.

In another embodiment of the invention, containment zone 16 is providedwith product monitoring and control means 21. Such monitoring means mayinclude an infrared spectrometer for detecting the presence of freeisocyanate groups and a microscopy device for determining the size ofthe particles. Preferably, the monitoring means are operably connectedto a computerized control device that functions to adjust processingconditions as necessary to produce particles of the requisite size.

The finely divided particulate polyurea powder, comprising from 5 to 15%of the total weight of base grease, is particularly suitable for forminggreases and is mixed with a base lubricating oil, comprising from 85 to95% of weight of base grease. The base lubricating fluid and polyureapowder are together placed in a conventional grease kettle or greasecontactor at ambient temperature where it is dispersed, sheared(milled), mixed and heated to a top temperature in the range of about150° C. to 175° C., cooled to a specified temperature then milled(homogenized) to form a finished homogenous grease.

Optionally, typical grease additives such as extreme pressure additives,rust inhibitors, antiwear compounds and the like may be added to themixture before milling.

In yet another embodiment of the invention, the finely powderedpolyurea, rather than packaged, is fed directly to a grease kettle formixing with a base oil and forming the mixture into a grease.

EXAMPLES

In the following Examples an air purge gun impingement device sold byContrast Equipment Co., Kansas City, Mo., was used. The mixing chambersused were obtained from Glas-Craft Inc., Indianapolis, Ind., and hadeither flat, rectangular or round dispensing patterns. Fourier TransformInfrared Spectrometer (“FTIR”) analysis of the reaction was conducted onappropriate product samples to determine whether the product containedfree isocyanate. The FTIR allows evaluating a product in process bymonitoring the spectral peaks. The standard ninhydrine test was used todetermine if a product contained unreacted amine.

Comparative Example 1

In this comparative example the reaction chamber had a flat mixingchamber. The amine used was cyclohexyl amine, and the diisocyanate usedwas methylene diphenylene diisocyanate. The orifice diameter for thereactants were 0.071 inches and 0.042 inches respectively. The reactantswere at ambient temperature (21° C.), and each was fed to the reactionchamber at 700 psig. Within 5 seconds the chamber clogged.

Comparative Example 2

The procedure of Comparative Example 1 was followed except a round mixchamber was used, and the pressure for each component was 1,000 psig.After about 3 seconds the chamber became clogged.

Example 1

In this example a (round mix chamber) was employed. The orifice diameterfor the amine feed was 0.109 inches, while the orifice diameter for thediisocyanate was 0.052 inches. The cyclohexyl amine was dissolved in anaphthenic oil having a kinematic viscosity @ 40 C. of 143.21 cSt. Theweight ratio of oil to amine was 1:1.2. Both the amine/oil feed and thediisocyanate feed were at 21 ° C. Then each were fed to the impingementdevice reaction chamber at 1000 psig. The resultant product had theconsistency of a finely divided polyurea powder in which the diluent oilwas dispersed. FTIR analysis failed to show a diisocyanate peak, and aninhydrine test failed to show free amine establishing completereaction. A sample of the product was mixed with an equal amount byweight of an oil typically used in formulating greases. The oil wasreadily incorporated in the product polyurea without any signs ofseparation.

Example 2

In this example a round mix chamber was used. The amine used was tallowamine which was dissolved in the naphthenic oil at a 2:1 oil to amineweight ratio. The diisocyanate was at 21° C. while the amine/oil feedwas heated to 32° C. Both feeds were fed to the reactor at 1800 psig.The resultant polyurea product had a powdery consistency. FTIR analysisshowed a diisocyanate peak at 2270⁻¹ cm of about 27% transmittance. Aswith the product of Example 1, this product blended very easily with agrease lubricating oil without any sign of oil separation.

Another attempt was made to manufacture completely reacted powder byusing the same round mix chamber, the oil to amine ratio was changed to1:1.5 and the feed pressure to the mix chamber was changed to 1000 psi.As a result, FTIR analysis failed to show a diisocyanate peak, and aninhydrine test failed to show free amine establishing completereaction. A sample of the product was mixed with an equal amount byweight of an oil typically used in formulating greases. The oil wasreadily incorporated in the product polyurea without any signs ofseparation.

An important aspect regarding prior art is that the structure of theparticles are comparatively different. The prior art formulation andmanufacturing of the polyurea powder results in the structure ofpolyurea particles being solid, compact and vary in size. U.S. Pat. No.5,314,982 and U.S. patent application No. 2006/0052261 are examples ofthe prior art. In comparison, polyurea particles made by impingementprocessing also vary in size but, the structure of the particle itselfis different. The polyurea particles manufactured, by virtue of theprocessing described in this patent, are porous and sponge like (foamycells) in their construction. The lubricating fluid used in the dilutionof the amine, as explained in the examples presented, is encapsulated orrather occupy the interstices of the particle as shown in FIG. 2. Asobserved during impingement processing, there is no oil pooling orseparation of the polyurea powder from oil during or after the powder ismade.

The polyurea powder is less dense than commercially available prior artpolyurea. The polyurea preferably has a density less than 6.5 lbs/gal,more preferably less than 6 lbs/gal and most preferably has a density ofless than 5.75 lbs/gal. In addition, the new polyurea powder has alarger surface are than prior art polyurea. Preferably, the polyureapowder has a specific surface area of more than 20 m²/g (measured by Hgporosimetry), more preferably 26 m²/g and most preferably more than 32m²/g.

A shelf life study was conducted to monitor the integrity of a typicalbatch of impinged polyurea powder over a 12 month period. Theobservations made from the shelf life study are as follows: in general,the polyurea powder still maintained its original integrity after 12months of storage, there was sign of excessive caking and no indicationvisibly or microscopically of oil leaching from the stored powder.

Regarding grease processing with the impinged preformed polyurea powder,the visibly large particles are easily broken apart, or fragmented, bythe shearing devises, mills and homogenizers, used in grease processing.Thus, over time during the base grease processing prior to toptemperature, the mass becomes thicker and more grease like as time andtemperature increase over the course of the proscribed manufacturingprocess.

Grease made with polyurea using the new method has improved properties.Table 2 shows the different properties of the two polyurea greases.Sample A is a grease made with conventional polyurea and higherpressures. Sample B is a grease made with new polyurea and with newmethod. As shown in Table 2, Sample A made with the old prior art methodof higher cook temperature and higher homogenization pressure (“Hog”)exhibits poor penetration properties. Sample B shows improved propertiesusing the new is method of producing grease.

TABLE 2 Properties of the Polyurea Grease SAMPLE A B TEST Hog pressure @6000 psig 1500 psig Cook temp, ° F. 400 320 Thickener content, % 12% 12%Appearance smooth dark brown smooth light brown Penetration Unworked 300294 Worked (60x) 324 292 Extended (10K) 400 100k = 353 Points change(60X to ext)  76  65 Dropping Point, ° C. 254 269

1. A method for preparing polyurea compounds by reacting amines andisocyanates in the presence of a liquid diluent in a high-pressureimpingement mixing device under conditions sufficient to produce apolyurea compound having the consistency of a powder and in whichckluent is dispersed, wherein the amities and isocvanates are fed to theimpingement device in a mole ratio of about 1:1 to about 2:1, at atemperature in the range of about O° C. to about 100° C. and a pressureabove about 500 psig through reactor orifices having an orifice of fromabout 0.030 to about 0.150 inches, wherein the reactor orifice of theamine and liquid diluent feed islarger than that for the isocyanate feedand is at least 0.109 inches in diameter.
 2. The method of claim 1wherein the liquid diluent is simultaneously mixed with the amines andisocyanates wherein each component exhibits substantially similardensities.
 3. The process of claim 2 wherein the liquiddiluent is inertto the amines and isocyanate.
 4. The process of claim 3 wherein thediluent is chosen from the group consisting of naphthenic, paraffinic,PAO, ester, PAG, carbon base solvents and any combination thereof. 5.The process of claim 4 wherein the ratio of diluent to amine is in therange of about 1:1 to about 3:1.
 6. The process of claim 5 wherein theparticles are passed through a containment zone equipped with FTIRmonitoring means.
 7. The process of claim 6 including process controlmeans operably connected to the monitoring means for adjustingprocessing conditions when necessary to maintain substantially completereaction.
 8. A method for making a particulate polyurea composition thatcan be homogenized into a grease at standard grease homogenizingconditions, the method comprising feeding a solution of an amine orisocyanate and a lubricating medium or solvent into an impingementreactor (mix chamber) while feeding a isocyanine into the reactor,wherein the mole ratio of amine to isocyanate is in the range of about1:1 to about 2:1 whereby a polyurea particulate composition having apowdery consistency is produced that can be homogenized into a greaseunder grease forming conditions at standard homogenizing conditions,wherein the amines and isocyanates are fed to the impingement reactor ata temperature in the range of about 0° C. to about 100° C. and apressure above about 500 psig through reactor orifices having an orificeof from about 0.030 to about 0.150 inches, wherein the reactor orificeof the amine and liquid diluent feed is larger than that for theisocyanate feed and is at least 0.109 inches in diameter.
 9. The methodof claim 8 wherein the weight ratio of lubricating medium or solvent tocomponent (reactants) is in the range of about 1:.5 to about 1:3. 10.The method of claim 9 wherein the feeding of individual component orcomponent solutions is conducted at pressures of from about 1000 psi toabout 1800 psi.
 11. The method of claim 10 wherein the feeding isconducted at temperatures in the range of from about 24° C. to about 55°C.
 12. A method for forming a grease comprising: mixing a baselubricating oil and a polyurea prepared by the method of any of claims8, 9, 10 or 11; heating the mixture of base oil and polyurea to atemperature in the range of about 150° C. to about 175° C.; andthereafter milling the heated mixture to form a homogenized grease. 13.The method of claim 1 wherein the isocyanate is a diisocyanate.
 14. Themethod of claim 8 wherein the isocyanate is a diisocyanate.